In the processing of wafers used in the manufacture of integrated circuits and the like, it is necessary in various processing steps to accomplish etching of certain areas of the wafer, to remove photoresist coating which may be applied to the wafer, and to otherwise clean the wafer. Prior art resist stripper processes are generally relatively slow, taking 30 to 60 minutes to remove the resist.
An apparatus which is directed toward these processing steps is disclosed in U.S. Pat. No. 3,990,462, issued to Elftmann, et al. As disclosed therein, wafers are disposed in cassettes which are in turn mounted on a rotary turntable. A central post defines a plurality of pairs of ports, each port being positioned to direct fluid therefrom onto an adjacent wafer as that wafer passes the port due to the rotary motion of the turntable. As disclosed in that patent, one port of each pair carries acid or water, while the other port carried gas, such as gaseous nitrogen, or air. Each pair of ports is positioned so that, with continuous fluid flow from that pair, an atomized fog-spray is provided to the wafer.
It will be understood that processing of such wafers must be done in an extremely even manner so that all parts of the wafer are processed properly and uniformly. This has been a problem in the type of apparatus disclosed in the above-cited patent. Furthermore, the processing of a wafer in such a system is relatively slow.
In U.S. Pat. No. 3,970,249 to Singer, secondary streams are alternatively applied to a stream of atomized particles by applying those particles to a substrate. The system thereof, however, is not applicable to processing semiconductor wafers, in particular the removal of material from a semiconductor wafer through etching, stripping or cleaning.
It is also known to utilize a semiconductor wafer processing apparatus which comprises a body defining first and second adjacent ports through which fluid may flow from the body, the ports being positioned so that fluid flow from the first port influences fluid flow from the second port, means for varying fluid flow from the first port, and means for supporting the wafer such that at least a portion of the fluid flow moves generally across a major surface of a so-supported wafer.
Of more general interest in this area are U.S. Pat. Nos. 3,769,992, to Wallestad and 3,727,620 to Orr.
Another process for cleaning semiconductor wafers is to contact them with a liquid solvent of the desired composition. The composition may be stirred or otherwise caused to flow across or against the surfaces of the wafers to provide somewhat of a washing action.
In the past, resist materials have been removed by utilizing one or more of the following: halogenated hydrocarbons, such as methylene chloride, sulfides such as dimethylsulfide, amines and their derivatives such as dimethylformamide, N-methyl-2-pyrrolidinone, glycol ethers such as ethylene glycol monomethyl ether, ethynol and the acetates thereof, ketones such as methyl ethyl ketone and acetone and materials such as isopropyl alcohol, sulfuric acid-hydrogen peroxide mixtures, ammonium persulfate and mixtures of caustic and phenol derivatives as well as by various other materials. Cleaning of the wafer utilizing such liquid solvents takes a good deal of time, often from 30 minutes to an hour residence time in a bath of the liquid.
Other methods of stripping resist include O.sub.2 plasmas, U.V./ozone, plus combinations, e.g., two operative processes. First a plasma step and then a liquid acid dip is the most common practice and the only way to do a complete resist stripping job.
There are several drawbacks with the use of the aforementioned resist material removing compositions. One of the major disadvantages with the aforementioned methods of stripping resist is that they do not remove deep UV baked, implant-hardened or plasma-hardened photoresist, or they leave behind traces of resist film and non-dissolved yield limiting contaminants originating from the liquid stripping compositions. Other disadvantages are undesirable flammability, volatility, odor or toxicity, drainage of large quantities of possibly dangerous chemicals in city sewer systems and attack of underlying metal films. Additionally, such strippers are not effective against resist materials that are subject to a severe post baking operation thereby limiting their usefulness. A disadvantage in instances where plasmas or U.V./ozone is used is that particulates are formed which must be liquid acid stripped. The plasma systems of choice are very complex (involving complicated vacuum systems and automation) and are also quite expensive.
The present invention is directed to solving one or more of the problems as set forth above.